Optimal Coordination of Dual-Setting Directional Over Current Relay in Microgrid Considering Multi-Parametric Characteristics

Conventional overcurrent protection schemes may not be sufficient to provide the complete protection of microgrids, especially in the islanded mode (ISM) of operation. Directional overcurrent relays (DOCRs) in microgrid may malfunction due to significant changes in fault current level and change in topology from grid-connected mode (GCM) to ISM. The novel contribution of this study is to determine the optimal settings of time-voltage-current-based dual-setting DOCRs with mixed inverse characteristics, valid in both GCM and ISM, without any miscoordination of relay pairs. The relay coordination problem is formulated as a mixed integer non-linear programming (MINLP) problem and optimally solved using an improved environmental adaption method (IEAM). The proposed relay coordination scheme has been tested on a 7-bus microgrid, the low-voltage section of the modified IEEE-14 bus benchmark system. The performance of the proposed protection scheme has been compared with the existing schemes, considering conventional DOCRs, time-voltage-current-based DOCRs, and dual-setting DOCRs.